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Questions and Answers
The first sensory changes in fish during storage primarily involve changes in texture and odour.
The first sensory changes in fish during storage primarily involve changes in texture and odour.
False
Rigor mortis in fish begins immediately after death when the muscles are completely relaxed.
Rigor mortis in fish begins immediately after death when the muscles are completely relaxed.
True
The onset of rigor mortis is uniform across all fish species regardless of handling and temperature.
The onset of rigor mortis is uniform across all fish species regardless of handling and temperature.
False
High temperatures consistently accelerate the onset of rigor mortis in tropical fish.
High temperatures consistently accelerate the onset of rigor mortis in tropical fish.
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Once rigor mortis resolves, the muscle becomes elastic again and retains its original firmness.
Once rigor mortis resolves, the muscle becomes elastic again and retains its original firmness.
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Glycogen reserves in fish have no effect on the timing of rigor mortis onset.
Glycogen reserves in fish have no effect on the timing of rigor mortis onset.
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Handling methods used for stunning fish have no impact on the onset of rigor mortis.
Handling methods used for stunning fish have no impact on the onset of rigor mortis.
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Temperature differences between sea and storage conditions affect the time from death to rigor onset in carp.
Temperature differences between sea and storage conditions affect the time from death to rigor onset in carp.
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Killing a fish by stunning results in the fastest onset of rigor mortis.
Killing a fish by stunning results in the fastest onset of rigor mortis.
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Cooking a fish pre-rigor results in a tough and dry texture.
Cooking a fish pre-rigor results in a tough and dry texture.
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White muscle in fish may shrink up to 52% of its original length during rigor.
White muscle in fish may shrink up to 52% of its original length during rigor.
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Filleting a fish in rigor results in poor filleting yield due to stiffness.
Filleting a fish in rigor results in poor filleting yield due to stiffness.
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The time from death to the end of rigor for unstressed cod at 0°C can last up to 96 hours.
The time from death to the end of rigor for unstressed cod at 0°C can last up to 96 hours.
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Fish stored in ice spoil less rapidly than fish stored under chilled conditions without ice.
Fish stored in ice spoil less rapidly than fish stored under chilled conditions without ice.
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Sensory evaluation of fish does not depend on the storage method used.
Sensory evaluation of fish does not depend on the storage method used.
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During phase 3 of fish deterioration, the flesh can develop a sickly sweet smell.
During phase 3 of fish deterioration, the flesh can develop a sickly sweet smell.
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Trimethylamine (TMA) is produced from the bacterial reduction of trimethyl-aminoxide (TMAO) in spoiled fish.
Trimethylamine (TMA) is produced from the bacterial reduction of trimethyl-aminoxide (TMAO) in spoiled fish.
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The characteristics of freshness in fish can vary based on the species and storage conditions.
The characteristics of freshness in fish can vary based on the species and storage conditions.
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Fish spoilage occurs primarily due to autolysis and microbial activity.
Fish spoilage occurs primarily due to autolysis and microbial activity.
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The highest quality of fish is indicated by a sensory evaluation score of 10.
The highest quality of fish is indicated by a sensory evaluation score of 10.
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ATP production in fish muscle tissue continues normally after death.
ATP production in fish muscle tissue continues normally after death.
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Enzymatic spoilage in fish happens after microbial spoilage.
Enzymatic spoilage in fish happens after microbial spoilage.
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Cod's pH drops from 6.8 to a range lower than 6.0 during post-mortem glycolysis.
Cod's pH drops from 6.8 to a range lower than 6.0 during post-mortem glycolysis.
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Fish display bright, iridescent pigmentation when they are spoiled.
Fish display bright, iridescent pigmentation when they are spoiled.
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Anaerobic conditions are sufficient for muscle energy production in living teleost fish.
Anaerobic conditions are sufficient for muscle energy production in living teleost fish.
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The sensory evaluation scale for fish ranges from 0 to 10, with the rejection level set at 4.
The sensory evaluation scale for fish ranges from 0 to 10, with the rejection level set at 4.
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Opaque mucus on fish gills indicates a high quality of fish.
Opaque mucus on fish gills indicates a high quality of fish.
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Octopine is the end-product from the anaerobic metabolism of cephalopods.
Octopine is the end-product from the anaerobic metabolism of cephalopods.
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Soft and flaccid fish flesh indicates high freshness.
Soft and flaccid fish flesh indicates high freshness.
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Fish flesh should be bluish and translucent for it to be considered fresh.
Fish flesh should be bluish and translucent for it to be considered fresh.
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The production of energy in post-mortem muscle is solely aerobic.
The production of energy in post-mortem muscle is solely aerobic.
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The coloration of fish organs such as kidneys should remain bright red when the fish is fresh.
The coloration of fish organs such as kidneys should remain bright red when the fish is fresh.
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Collagenase enzymes are believed to originate from the muscles of prawns.
Collagenase enzymes are believed to originate from the muscles of prawns.
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The enzyme TMAO-ase is responsible for converting TMAO into dimethylamine and formaldehyde.
The enzyme TMAO-ase is responsible for converting TMAO into dimethylamine and formaldehyde.
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The removal of the kidney is not crucial for minimizing toughening in gadoid fish during frozen storage.
The removal of the kidney is not crucial for minimizing toughening in gadoid fish during frozen storage.
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The ultimate rigor pH in large mackerel can be as low as 5.8-6.0.
The ultimate rigor pH in large mackerel can be as low as 5.8-6.0.
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Physical abuse to fish before freezing can accelerate the production of formaldehyde.
Physical abuse to fish before freezing can accelerate the production of formaldehyde.
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Storing fish at a temperature of less than -30°C helps prevent the autolytic production of formaldehyde.
Storing fish at a temperature of less than -30°C helps prevent the autolytic production of formaldehyde.
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Fish muscle typically contains a higher level of glycogen than mammalian muscle.
Fish muscle typically contains a higher level of glycogen than mammalian muscle.
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Rigor mortis results in a decrease in muscle ATP levels below 1.0 µmoles/g.
Rigor mortis results in a decrease in muscle ATP levels below 1.0 µmoles/g.
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The enzymatic activity of TMAO demethylase is higher in white muscle compared to red muscle.
The enzymatic activity of TMAO demethylase is higher in white muscle compared to red muscle.
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Temperature fluctuations during frozen storage have no effect on the level of formaldehyde produced.
Temperature fluctuations during frozen storage have no effect on the level of formaldehyde produced.
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Bleeding of fish has no effect on the post mortem production of lactic acid.
Bleeding of fish has no effect on the post mortem production of lactic acid.
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Autolysis in fish can lead to a gradual production of bitterness due to breakdown of ATP.
Autolysis in fish can lead to a gradual production of bitterness due to breakdown of ATP.
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The K value is a freshness index based on the degradation of ATP-related compounds in fish muscle.
The K value is a freshness index based on the degradation of ATP-related compounds in fish muscle.
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Removing calcium can prevent the activation of calpain, which is involved in muscle softening.
Removing calcium can prevent the activation of calpain, which is involved in muscle softening.
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ATP is solely responsible for muscle contraction in fish.
ATP is solely responsible for muscle contraction in fish.
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Glycolytic enzymes are responsible for the production of lactic acid, resulting in a decrease in the pH of fish tissue.
Glycolytic enzymes are responsible for the production of lactic acid, resulting in a decrease in the pH of fish tissue.
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A fish in rigor mortis becomes too stiff to be filleted or processed easily.
A fish in rigor mortis becomes too stiff to be filleted or processed easily.
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The relationship between muscle toughness and pH is direct; higher pH levels lead to increased toughness.
The relationship between muscle toughness and pH is direct; higher pH levels lead to increased toughness.
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Sodium chloride has a strong inhibitory effect on enzyme activity.
Sodium chloride has a strong inhibitory effect on enzyme activity.
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Cathepsin D is primarily responsible for the softening of salmon muscle during spawning migration.
Cathepsin D is primarily responsible for the softening of salmon muscle during spawning migration.
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Chiba et al. (1991) found that non-struggling fish have a greater pH drop compared to struggling fish.
Chiba et al. (1991) found that non-struggling fish have a greater pH drop compared to struggling fish.
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Freezing and thawing fish tissue enhances autolytic activity of membrane-bound enzymes.
Freezing and thawing fish tissue enhances autolytic activity of membrane-bound enzymes.
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The degradation of ATP catabolites progresses at the same rate across all fish species.
The degradation of ATP catabolites progresses at the same rate across all fish species.
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Calpains require high concentrations of calcium to be activated.
Calpains require high concentrations of calcium to be activated.
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IMP is associated with a desirable fresh fish flavor.
IMP is associated with a desirable fresh fish flavor.
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Calpains in fish and crustaceans have similar digestive capabilities.
Calpains in fish and crustaceans have similar digestive capabilities.
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Loss of water in fish muscle during cooking is beneficial for its texture.
Loss of water in fish muscle during cooking is beneficial for its texture.
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Stressing fish before capture leads to an increase in glycogen stores.
Stressing fish before capture leads to an increase in glycogen stores.
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Collagenases are responsible for the breakdown of myocytes during chilled storage.
Collagenases are responsible for the breakdown of myocytes during chilled storage.
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The breaking strength of fish muscle is negatively correlated with cathepsin L activity.
The breaking strength of fish muscle is negatively correlated with cathepsin L activity.
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The softening of muscle during resolution of rigor is a completely understood process.
The softening of muscle during resolution of rigor is a completely understood process.
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Postmortem changes in freshness are solely indicated by the degradation of nucleotide catabolites.
Postmortem changes in freshness are solely indicated by the degradation of nucleotide catabolites.
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Type V collagen solubilization leads to increased instrumental measurements of fish muscle texture.
Type V collagen solubilization leads to increased instrumental measurements of fish muscle texture.
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Molecular weight of myosin heavy chain fragments formed by fish calpains is approximately 150,000 Da.
Molecular weight of myosin heavy chain fragments formed by fish calpains is approximately 150,000 Da.
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Cathepsins are responsible for detrimental changes in texture for fermented fish products.
Cathepsins are responsible for detrimental changes in texture for fermented fish products.
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Tropical fish are more susceptible to calpain autolysis than fish adapted to colder temperatures.
Tropical fish are more susceptible to calpain autolysis than fish adapted to colder temperatures.
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The activity of calpains is maximized at high pH levels.
The activity of calpains is maximized at high pH levels.
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Proteolytic enzymes secreted by parasites have been conclusively identified in infected fish muscle.
Proteolytic enzymes secreted by parasites have been conclusively identified in infected fish muscle.
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The rates of formation and breakdown of IMP were the same in both sterile and non-sterile samples of cod tissue.
The rates of formation and breakdown of IMP were the same in both sterile and non-sterile samples of cod tissue.
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Bacterial nucleoside phosphorylase has no impact on the conversion of Iino to Hex.
Bacterial nucleoside phosphorylase has no impact on the conversion of Iino to Hex.
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The breakdown rate of nucleotide catabolites is greater in non-sterile fillets than in sterile fillets.
The breakdown rate of nucleotide catabolites is greater in non-sterile fillets than in sterile fillets.
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The presence of autolytic enzymes is enhanced when fish are physically handled.
The presence of autolytic enzymes is enhanced when fish are physically handled.
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Surette et al. were able to recover nucleoside phosphorylase from freshly killed cod.
Surette et al. were able to recover nucleoside phosphorylase from freshly killed cod.
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Belly-bursting in pelagic fish is primarily influenced by biological factors such as fish size and feed content.
Belly-bursting in pelagic fish is primarily influenced by biological factors such as fish size and feed content.
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Cathepsins are a type of proteolytic enzyme that remains inactive in living tissue.
Cathepsins are a type of proteolytic enzyme that remains inactive in living tissue.
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The breakdown of proteins through autolysis can lower the nutritional value of fish.
The breakdown of proteins through autolysis can lower the nutritional value of fish.
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Autolytic changes cause significant softening of fish tissues primarily due to nucleoside phosphorylase activity.
Autolytic changes cause significant softening of fish tissues primarily due to nucleoside phosphorylase activity.
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The conversion of inosine to hypoxanthine is inferred to be useful for determining freshness in various fish species.
The conversion of inosine to hypoxanthine is inferred to be useful for determining freshness in various fish species.
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Proteolytic breakdown in fish muscle leads to the production of low molecular weight peptides.
Proteolytic breakdown in fish muscle leads to the production of low molecular weight peptides.
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Fish should be stored in deeper boxes for optimal preservation and to minimize autolysis.
Fish should be stored in deeper boxes for optimal preservation and to minimize autolysis.
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Freezing and thawing processes have minimal effect on the autolysis of fish tissue.
Freezing and thawing processes have minimal effect on the autolysis of fish tissue.
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What occurs during the resolution of rigor mortis in fish?
What occurs during the resolution of rigor mortis in fish?
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How does the temperature influence rigor mortis in cod fish?
How does the temperature influence rigor mortis in cod fish?
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What effect do starved fish have on the rigor mortis onset?
What effect do starved fish have on the rigor mortis onset?
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Which statement accurately describes the relationship between handling methods and rigor mortis onset?
Which statement accurately describes the relationship between handling methods and rigor mortis onset?
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How does the difference between sea temperature and storage temperature affect rigor mortis in carp?
How does the difference between sea temperature and storage temperature affect rigor mortis in carp?
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What is the primary consequence of strong rigor tensions in cod fish?
What is the primary consequence of strong rigor tensions in cod fish?
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What sensory element is NOT typically used to evaluate the freshness of fish?
What sensory element is NOT typically used to evaluate the freshness of fish?
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Which factor might inhibit the rate of rigor mortis onset in fish?
Which factor might inhibit the rate of rigor mortis onset in fish?
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What is the impact of cooking fish that is still in rigor mortis?
What is the impact of cooking fish that is still in rigor mortis?
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How long can the onset of rigor mortis take for unstressed cod at 0°C?
How long can the onset of rigor mortis take for unstressed cod at 0°C?
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Which of the following contributes to the poor filleting yield when a fish is filleted in rigor?
Which of the following contributes to the poor filleting yield when a fish is filleted in rigor?
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What characterizes the flesh of fish post-rigor?
What characterizes the flesh of fish post-rigor?
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Which factor is most crucial for maintaining fish quality during frozen storage?
Which factor is most crucial for maintaining fish quality during frozen storage?
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What sensory change occurs during phase 3 of fish deterioration?
What sensory change occurs during phase 3 of fish deterioration?
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Which statement about handling methods affecting rigor mortis is accurate?
Which statement about handling methods affecting rigor mortis is accurate?
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During which phase is fish characterized by a neutral taste and no off-flavours?
During which phase is fish characterized by a neutral taste and no off-flavours?
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What happens to dark muscle when stored post-mortem?
What happens to dark muscle when stored post-mortem?
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What is indicated by a sensory evaluation score of 3 in fish quality assessment?
What is indicated by a sensory evaluation score of 3 in fish quality assessment?
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What characteristic indicates the highest quality in fish appearance?
What characteristic indicates the highest quality in fish appearance?
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Which condition of fish flesh is indicative of spoilage?
Which condition of fish flesh is indicative of spoilage?
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What happens to the color of fish kidneys and blood after spoilage?
What happens to the color of fish kidneys and blood after spoilage?
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How does the pH of cod muscle change during post-mortem glycolysis?
How does the pH of cod muscle change during post-mortem glycolysis?
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What is characterized by the accumulation of lactic acid and a drop in tissue pH?
What is characterized by the accumulation of lactic acid and a drop in tissue pH?
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What does the sensory evaluation scale for fish indicate when the score is set at 4?
What does the sensory evaluation scale for fish indicate when the score is set at 4?
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What occurs immediately after a fish dies regarding muscle energy production?
What occurs immediately after a fish dies regarding muscle energy production?
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Which type of spoilage occurs predominantly in certain fish species like squid and herring?
Which type of spoilage occurs predominantly in certain fish species like squid and herring?
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What is the primary consequence of ATP depletion in fish muscle post-mortem?
What is the primary consequence of ATP depletion in fish muscle post-mortem?
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Which of the following statements about tissue condition after spoilage is false?
Which of the following statements about tissue condition after spoilage is false?
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What indicates a good sensory evaluation score for fish?
What indicates a good sensory evaluation score for fish?
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How does temperature affect the rate of rigor mortis onset in fish?
How does temperature affect the rate of rigor mortis onset in fish?
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How does a fish's condition change immediately after death?
How does a fish's condition change immediately after death?
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The production of energy in fish muscle post-mortem relies primarily on which process?
The production of energy in fish muscle post-mortem relies primarily on which process?
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What primarily accelerates the conversion of Iino to Hex in non-sterile cod samples?
What primarily accelerates the conversion of Iino to Hex in non-sterile cod samples?
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What effect does physical handling have on chilled fish?
What effect does physical handling have on chilled fish?
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What enzyme is believed to be significantly involved in the autolytic degradation of fish tissue?
What enzyme is believed to be significantly involved in the autolytic degradation of fish tissue?
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How do variations in Hx levels among different fish species affect their freshness determination?
How do variations in Hx levels among different fish species affect their freshness determination?
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What is a major consequence of belly-bursting in pelagic fish species?
What is a major consequence of belly-bursting in pelagic fish species?
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What is the role of cathepsins in living fish tissue?
What is the role of cathepsins in living fish tissue?
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Which practice is crucial for minimizing autolytic processes during fish storage?
Which practice is crucial for minimizing autolytic processes during fish storage?
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In the context of autolysis, what happens to the tissue of bulk-stored capelin?
In the context of autolysis, what happens to the tissue of bulk-stored capelin?
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What impact does the freezing/thawing cycle have on herring compared to biological factors?
What impact does the freezing/thawing cycle have on herring compared to biological factors?
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What might occur when nucleoside phosphorylase is not recovered from freshly killed cod?
What might occur when nucleoside phosphorylase is not recovered from freshly killed cod?
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What effect do low molecular weight peptides have on fish muscle after autolysis?
What effect do low molecular weight peptides have on fish muscle after autolysis?
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What storage practice is recommended for maintaining the quality of iced fish?
What storage practice is recommended for maintaining the quality of iced fish?
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What is a significant characteristic of autolytic enzymes in fish tissues?
What is a significant characteristic of autolytic enzymes in fish tissues?
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What is the primary factor affecting the amount of lactic acid produced in fish muscle after death?
What is the primary factor affecting the amount of lactic acid produced in fish muscle after death?
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Which fish species is mentioned as having an ultimate rigor pH as low as 5.4-5.6?
Which fish species is mentioned as having an ultimate rigor pH as low as 5.4-5.6?
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What effect does bleeding fish have on lactic acid production post mortem?
What effect does bleeding fish have on lactic acid production post mortem?
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What happens to the net surface charge of muscle proteins as the pH drops in fish muscle?
What happens to the net surface charge of muscle proteins as the pH drops in fish muscle?
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What is the primary consequence of the action of collagenase enzymes in chilled prawns?
What is the primary consequence of the action of collagenase enzymes in chilled prawns?
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Which organ is thought to be the source of collagenase enzymes in prawns?
Which organ is thought to be the source of collagenase enzymes in prawns?
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During autolysis, what happens to ATP levels in fish muscle after death?
During autolysis, what happens to ATP levels in fish muscle after death?
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What is the relationship between muscle toughness and pH in fish as indicated in the content?
What is the relationship between muscle toughness and pH in fish as indicated in the content?
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What is the role of the enzyme TMAO-ase in fish tissue?
What is the role of the enzyme TMAO-ase in fish tissue?
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Which ATP degradation product is responsible for the desirable fresh fish flavor?
Which ATP degradation product is responsible for the desirable fresh fish flavor?
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Which muscle type has a higher rate of TMAO demethylase activity?
Which muscle type has a higher rate of TMAO demethylase activity?
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What effect does formaldehyde have on fish muscle when produced during storage?
What effect does formaldehyde have on fish muscle when produced during storage?
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What occurs to fish muscle that is in rigor mortis regarding its physical handling?
What occurs to fish muscle that is in rigor mortis regarding its physical handling?
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What storage condition is recommended to minimize the production of formaldehyde in fish?
What storage condition is recommended to minimize the production of formaldehyde in fish?
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What conclusion can be drawn about the K value in relation to fish freshness?
What conclusion can be drawn about the K value in relation to fish freshness?
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What is a significant effect of rough handling of fish prior to freezing?
What is a significant effect of rough handling of fish prior to freezing?
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What role does calcium play in muscle contraction in fish?
What role does calcium play in muscle contraction in fish?
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How does pre-capture stress affect the pH of fish muscle over time?
How does pre-capture stress affect the pH of fish muscle over time?
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Which autolytic change leads to a loss of fresh fish flavor?
Which autolytic change leads to a loss of fresh fish flavor?
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What is a recommended practice to avoid toughening of minced fish during frozen storage?
What is a recommended practice to avoid toughening of minced fish during frozen storage?
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Which enzyme is involved in the significant softening of muscle tissue during the resolution of rigor?
Which enzyme is involved in the significant softening of muscle tissue during the resolution of rigor?
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What is the relationship between temperature fluctuations during storage and formaldehyde production?
What is the relationship between temperature fluctuations during storage and formaldehyde production?
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Why is ATP considered important for muscle contraction in living fish, aside from providing energy?
Why is ATP considered important for muscle contraction in living fish, aside from providing energy?
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How does muscle tissue in rigor mortis respond to heating during cooking?
How does muscle tissue in rigor mortis respond to heating during cooking?
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What effect does the presence of 5% sodium chloride have on the enzyme activity of Reddi's enzyme?
What effect does the presence of 5% sodium chloride have on the enzyme activity of Reddi's enzyme?
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Which cathepsin is primarily implicated in the softening of salmon muscle during spawning migration?
Which cathepsin is primarily implicated in the softening of salmon muscle during spawning migration?
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What property of cathepsin L was demonstrated to correlate with muscle texture in salmon?
What property of cathepsin L was demonstrated to correlate with muscle texture in salmon?
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How do calpains differ from cathepsins regarding their activity in fish muscle?
How do calpains differ from cathepsins regarding their activity in fish muscle?
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What role do calpains play in the texture of fish muscle during storage?
What role do calpains play in the texture of fish muscle during storage?
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What is one consequence of freezing and thawing fish muscle regarding enzyme activity?
What is one consequence of freezing and thawing fish muscle regarding enzyme activity?
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What factor greatly influences calpain activity in fish species?
What factor greatly influences calpain activity in fish species?
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What is the primary substrate that calpains digest in vertebrate muscle?
What is the primary substrate that calpains digest in vertebrate muscle?
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What is a notable effect of collagenase enzymes during fish storage?
What is a notable effect of collagenase enzymes during fish storage?
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What happens to the type V collagen in chilled trout muscle over time?
What happens to the type V collagen in chilled trout muscle over time?
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At which temperature does gaping become inevitable in Atlantic cod?
At which temperature does gaping become inevitable in Atlantic cod?
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What is the primary function of the myocommata in teleost fish?
What is the primary function of the myocommata in teleost fish?
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How does the enzymatic activity of calpains in fish compare to that in mammals?
How does the enzymatic activity of calpains in fish compare to that in mammals?
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What condition influences the cleavage rate of myosin by fish calpains?
What condition influences the cleavage rate of myosin by fish calpains?
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Study Notes
Postmortem Changes in Fish
Sensory Changes
- Sensory changes include alterations in appearance, odor, texture, and taste during fish storage.
- Initial changes involve loss of characteristic taste, developing within the first few days in ice.
- Rigor mortis sets in post-mortem, transitioning fish muscle from a relaxed state to a stiff, inflexible condition.
- Onset and resolution of rigor mortis depend on species, temperature, handling, and fish size.
- For cod, high temperatures accelerate rigor mortis, while in tropical fish, a colder temperature may expedite rigor onset.
- Pre-rigor filleting retains better texture and yield compared to post-rigor.
- Consumption texture differs notably between pre-rigor (soft) and post-rigor (tough but moist) fish.
- Sensory evaluation of raw fish includes assessing appearance, texture, and odor, affected by storage method (iced vs. chilled).
- Fish stored under different methods exhibit varying levels of quality and spoilage indicators utilizing a scoring system (0 to 3 for raw quality).
Autolytic Changes
- Autolysis refers to self-digestion processes influenced by enzymatic and microbial activity in fish spoilage.
- Enzymatic changes can happen independently of bacterial spoilage initial stages and predominate in some species.
- The interruption of oxygen supply after death leads to anaerobic respiration, restricting energy production in muscle tissues.
- Limited ATP production results in lactic acid accumulation, lowering muscle pH, impacting texture and water-holding capacity.
- Rigor mortis ensues when ATP levels drop significantly, impeding muscle contracts.
- pH drops during rigor mortis, with values ranging from 6.1-6.5 in cod, whereas some species might drop as low as 5.4.
Bacteriological Changes
- Not covered directly but generally, postmortem spoilage often results from microbial activity, exacerbated by the initial autolytic changes.
Lipid Oxidation and Hydrolysis
- Not detailed within the provided text but typically involves chemical reactions leading to spoilage in fish oils, affecting flavor and shelf life.
Nucleotide Degradation in Fish
- Variability in nucleotide degradation patterns exists among fish species, notably in the levels of hypoxanthine (Hx).
- Hx determination is not reliable for species like swordfish and redfish due to significant interspecies differences.
Autolysis in Fish Handling
- Physical handling accelerates autolytic changes in chilled fish; sterile fillets show a higher breakdown rate of nucleotide catabolites compared to non-sterile whole gutted fish.
- Crushing fish during storage can impact edibility and filleting yields, stressing the importance of proper handling practices.
- Recommended storage: Iced fish should not be stacked in boxes deeper than 30 cm to minimize autolysis.
Proteolytic Enzymes and Autolysis
- Autolytic changes include proteolysis which softens fish tissue, notably prevalent in fatty species like herring and capelin during summer feeding.
- Autolysis enhances spoilage bacteria growth, reducing commercial value and affecting the nutritional quality of fish like capelin.
- Studies showed that proteolytic enzymes can be inhibited by potato extracts, promoting preservation of nutritional value in fishmeal.
Cathepsins and Muscle Softening
- Cathepsins, mainly cathepsins D and L, are acid proteases involved in autolytic degradation, being inactive in live tissues but active after physical damage or freezing.
- Cathepsin L plays a significant role in softening salmon muscle and correlates well with muscle texture measurements.
- Activity of cathepsins increases following freezing/thawing due to cell membrane breakdown, affecting softening rates.
Calpains in Fish Autolysis
- Calpains, calcium-activated intracellular proteases, contribute to autolysis in fish muscle, though they’re primarily known for their role in mammal meat aging.
- Active at physiological pH, calpains are implicated in the softening of fish during chilled storage and are specific to certain myofibrillar proteins.
Collagenases and Connective Tissue
- Collagenase enzymes target connective tissue, leading to gaping or breakdown of muscle structure during prolonged storage.
- Instrumental texture measurements decline as collagen, especially type V, is solubilized in chilled fish.
TMAO and Autolytic Changes
- Trimethylamine oxide (TMAO) conversion to dimethylamine and formaldehyde by muscle enzymes can toughen fish muscle, impacting quality.
- TMAO-demethylase activity is highest in gadoid fishes, particularly in dark muscle, emphasizing the importance of removing organ tissues to prevent toughening.
Prevention of Autolytic Effects
- Optimal storage conditions are crucial for minimizing autolysis: keeping fish below -30°C and avoiding rough handling are key strategies.
- Rough handling or physical damage are the most significant factors accelerating autolysis in fish products.
Postmortem Changes in Fish
Sensory Changes
- Sensory changes involve appearance, odour, texture, and taste.
- Rigor mortis is a significant postmortem change, initially resulting in a relaxed muscle that later becomes stiff.
- Onset and resolution of rigor mortis vary by species and are influenced by factors like temperature and handling.
- Higher temperatures can speed up rigor mortis, potentially causing gaping in fish like cod.
- Fish with reduced glycogen due to starvation or stress experience quicker rigor onset.
- Pre-rigor filleting allows for better texture; post-rigor fish becomes tough, while cooking pre-rigor yields softer texture.
- Sensory evaluations of fish consider appearance, texture, and odour, with characteristic changes observable over time.
- Fish stored on ice undergo a four-phase deterioration:
- Phase 1: Fresh with sweet taste, optimal 2-3 days post-catch.
- Phase 2: Neutral odour and taste, still pleasant texture.
- Phase 3: Signs of spoilage with unpleasant smells and altered texture.
- Phase 4: Spoiled and putrid characteristics.
- Freshness evaluation scales assess sensory attributes based on EEC regulations.
Autolytic Changes
- Autolysis, or "self-digestion," is crucial in fish spoilage, primarily divided into bacterial and enzymatic spoilage.
- Lack of oxygen after death restricts energy production, leading to anaerobic metabolism.
- Glycogen is the main energy source used for ATP production, which declines during rigor mortis.
- The pH of muscle drops from around 6.8 to as low as 5.4-6.5 during postmortem, impacting texture and water-holding capacity.
- Stress before capture decreases glycogen reserves, leading to differences in postmortem pH levels.
- Muscles in rigor mortis lose moisture when cooked, leading to undesirable texture changes.
- ATP degradation during rigor mortis contributes to texture and quality changes; rapid degradation affects perceived freshness.
- Autolytic changes and nucleotide catabolism are crucial for assessing fish freshness, with specific ATP breakdown products used as indicators.
- IMP is linked to desirable fresh fish flavour, while Hx contributes to bitter off-flavours in spoiled fish.
- Freshness indices based on ATP breakdown may not always correlate with sensory quality due to variability among species.### Nucleotide Degradation Variability
- Nucleotide degradation varies significantly between fish species, impacting the utility of Hx determination for certain species like swordfish and redfish.
- Changes in nucleotide levels (IMP, Ino, Hx) occur differently in sterile and non-sterile cod fillets stored at 3°C.
Autolytic Changes
- Physical handling accelerates autolytic changes in chilled fish; sterile fillets show faster breakdown of nucleotide catabolites compared to non-sterile gutted fish.
- Crushing from ice or other fish adversely affects fish edibility and filleting yields, highlighting the role of autolytic processes in fish quality.
- Iced fish storage capacity should not exceed 30 cm depth to minimize autolysis.
Proteolytic Enzymes
- Proteases from fish muscle can lead to significant tissue softening, notably in fatty fish such as herring and capelin.
- The phenomenon of belly-bursting in pelagic species is exacerbated during summer feeding on copepods and euphausiids.
- Autolysis increases the risk of spoilage bacteria growth in bulk-stored fish, adversely affecting commercial value.
- Presence of microbially produced biogenic amines lowers nutritive value.
- Potato extracts can inhibit proteolysis and microbial growth, preserving nutritional quality.
Cathepsins
- Cathepsins, acid proteases, are crucial in autolytic degradation after physical injury or freezing/thawing.
- Cathepsin D is active at pH 3-8, while cathepsin L, more efficient at neutral pH, is associated with softening effects in salmon during spawning.
Calpains
- Calpains are intracellular proteases involved in post-mortem muscle autolysis, tenderizing meat by digesting z-line proteins.
- Fish calpains are more active in lower temperatures and affect muscle texture based on species-specific characteristics.
- Both µ-calpain and m-calpain are active in fish muscle, with implications for commercial fish quality.
Collagenases
- Collagenases target connective tissue in fish, leading to texture deterioration during storage.
- Solubilization of type V collagen correlates with loss of fish texture, leading to gaping in fillets.
- The hepatopancreas in prawns is thought to be the source of collagenase enzymes that contribute to texture softening.
Autolytic Changes During Frozen Storage
- TMAO breakdown occurs through both bacterial action and specific enzymatic activity in fish, leading to dimethylamine (DMA) and formaldehyde (FA) production.
- FA can cause toughening of muscle proteins, impacting quality negatively.
- TMAO-ase, primarily found in gadoid fish, is responsible for tougher textures in frozen products.
- It is essential to ensure gadoid minced fish is free of organ tissues to prevent toughening during storage.
Prevention of Autolytic Changes
- Physical disruption of muscle cells is the leading cause of autolytic changes; minimizing rough handling can significantly enhance fish quality.
- Recommended practices include avoiding temperature fluctuations during storage, preventing physical damage, and storing at temperatures below -30°C to inhibit enzyme activity.
Summary of Autolytic Changes in Chilled Fish
- The effectiveness of preventing autolytic changes lies in understanding the roles of various enzymes and the impact of environmental conditions on fish quality.
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Description
Explore the fascinating changes that fish undergo postmortem, focusing on sensory, autolytic, bacteriological, and oxidative changes. Understand how these factors affect appearance, odour, texture, and taste during storage. Perfect for those studying fish biology and food science.
